Advances in Materials Science and Engineering
Volume 2008 (2008), Article ID 406067, 6 pages
doi:10.1155/2008/406067
Research Article

Coesite Formation at Ambient Pressure and Low Temperatures

J. R. Martínez,1,2 A. Vázquez-Durán,3 G. Martínez-Castañón,4 G. Ortega-Zarzosa,1 S. A. Palomares-Sánchez,1 and Facundo Ruiz1

1Facultad de Ciencias, Universidad Autónoma de San Luis Potosí, 78000 San Luis Potosí, Mexico
2Departamento de Físico-Matemáticas, Universidad Autónoma de San Luis Potosí, 78000 San Luis Potosí, Mexico
3Centro de Investigación en Óptica, A.C., 37150 León, Gto., Mexico
4Facultad de Estomatología, Universidad Autónoma de San Luis Potosí, 78000 San Luis Potosí, Mexico

Received 19 May 2008; Revised 16 July 2008; Accepted 21 July 2008

Academic Editor: Ming-Xing Zhang

Copyright © 2008 J. R. Martínez et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Partial crystallization of silica xerogel in the form of coesite has been obtained at low-pressure conditions and temperatures of ∼565∘C, in samples containing chlorophyll aggregates dispersed in amorphous silica. Silica xerogel samples were prepared by the sol-gel method using an ethanol:H2O:TEOS molar ratio of 4:11.6:1 and loaded with extracts from frozen spinach leaves. The silica xerogel microstructure of the powders was studied as a function of annealing temperature. It was found that partial crystallization of the glass matrix in the form of coestite was obtained at lower pressure than those specified by the phase diagram. Chlorophyll aggregates were added to the starting solutions which, upon thermal treatments, form small colloidal particles in the glass matrix. The presence of coesite is corroborated by the Rietveld refinement method.